1. Field of the Invention
This invention relates to methods for repairing aircraft window laminates comprising two or more plies of the same or different material. More particularly, this invention relates to methods for introducing an adhesive in the delaminated area between the plies which have become separated. This invention also relates to methods for repairing electrically conductive plies and heat control sensors of laminates.
2. Description of the Background Art
A laminate is a composition of material which usually includes three or more plies of material; typically, two or more layers of material having the desired characteristics and an adhesive layer which bonds such nonadhesive layers together. The aspect of bonding two materials together, each material having the same or different characteristics, can yield a laminate which is much more desirable for a particular purpose than a sheet of homogeneous material. Accordingly, the use of laminates has proliferated in the past and will continue to proliferate for many years to come.
One major disadvantage to laminates is their tendency to delaminate under certain conditions or after a certain length of time. Upon delamination, the desired characteristics of the laminate (strength, durability, light transmittance characteristics, etc.) are substantially and adversely affected. Further, once the delamination forms, it rapidly spreads throughout the entire laminate. These problems are so acute in the industry that it is common practice to virtually replace the entire laminate even when only two plies have become delaminated. Obviously, the requirement for replacing the entire laminate is extremely costly not only from the pure expense involved but also with respect to down time of the apparatus which utilizes the laminate.
Various efforts have been made to repair a delaminated laminate. Those efforts have basically included methods for cutting into the laminate to remove the delaminated area and then rebonding a new section of a laminate or homogeneous material in the opening thus formed. The other methods have included various techniques for bonding a patch over the delaminated area, or affixing a patch about the delaminated area by means of rivets or other fasteners. Some techniques have included a combination of both bonding and affixing of the patch about the delaminated area. When the delaminated area includes a perforated area, it is common practice to adhere a sheet of fiberglass material over the patch to prevent contamination and moisture from passing through the perforation.
A particular type of industry in which laminates are widely used, is the transparency industry for making aircraft windows and the like. In this particular industry, the aircraft window typically comprises two to five plies of an acrylic material which are bound together by interposed adhesive plies. A scratch resistive ply, such as glass, is then affixed to the opposing side of the acrylic plies by similar adhesive plies. Usually, an electrically conductive ply is meshed between the outer glass ply and the outer-most acrylic ply to enable electrical current to flow therethrough to heat the window to a particular temperature as determined by a heat control sensor, thereby preventing ice formation on the window during flight.
The primary disadvantage to transparency laminates is their tendency to delaminate about their peripheral edges within two to five years of service. The delamination at the edges of the transparency quickly grows to such a point that the transparency has to be discarded and a new one reinstalled. It is contemplated that this delamination occurs at such an early stage due to the inherent environment in which the aircraft are exposed; namely, jet fuel contaminants and moisture ingress through seals of the frame, extreme temperatures and a certain amount of flexing of the laminate.
Another disadvantage to transparency laminates, particularly aircraft laminates, is that the degradation of the electrical interconnect between the electrical bus bars and the electrically conductive ply. Usually, upon sufficient degradation, arcing occurs between the bus bars and the electrically conductive ply causing non-uniform power gradient throughout the electrically conductive ply. Thus, "hot spots" are created at various portions of the electrically conductive ply. Moreover, electrical arcing occurs between the bus bars and the electrically conductive ply thereby also creating "hot spots" along the interconnection. Excessive heat at such "hot spots" can become so severe that the acrylic plies are damaged. Clouding of the acrylic plies usually also results.
Finally, another disadvantage of aircraft window laminates is the usual failure of the heat control sensor which controls the amount of power flowing to the electrically conductive ply. Since the heat sensor is imbedded in the laminate, the failure of the sensor usually results in discarding the entire laminate.
It is an object of this invention to provide an improved method which overcomes the aforementioned inadequacies of the prior art methods and provides an improvement which is a significant contribution to the advancement of the art of repairing laminates.
Another object of this invention is to provide a method for repairing laminates in which the delaminated plies are adhesively bound together to substantially achieve the original characteristics of the laminate.
Another object of this invention is to provide a method for repairing laminates which can be performed at a cost substantially less than the original cost of the laminate.
Another object of this invention is to provide a method for repairing laminates in which an adhesive, compatible with the adjoining plies, is introduced into the delaminated area.
Another object of this invention is to provide a method for repairing a laminate which eliminates the need to cut into the laminate and remove the delaminated area.
Another object of this invention is to provide a method for repairing a laminate which eliminates the need to apply a patch to the delaminated area in order to repair the same.
Another object of this invention is to provide a method for repairing a laminate in which the laminate has become delaminated about its peripheral edges.
Another object of this invention is to provide a method for repairing transparency laminates commonly used in the aircraft industry.
Another object of this invention is to provide a method for repairing aircraft transparency laminates without adversely affecting the electrical heating ply positioned within the transparency laminate.
Another object of this invention is to provide a method for repairing the electrically conductive ply of an aircraft transparency laminate to increase the uniformity of the power gradient across the ply thereby minimizing "hot spots" in the laminate.
Another object of this invention is to provide a method for repairing the electrical interconnect between the bus bars and the electrically conductive ply of an aircraft transparency laminate.
Another object of this invention is to provide a method for installing a new heat control sensor to substitute for the original, now defective, heat control sensor of an aircraft transparency laminate.
Another object of this invention is to provide a method for positioning the heat control sensor of an aircraft transparency laminate to one of the hotter areas of the laminate so that the laminate is not damaged from overheating.
The foregoing has outlined some of the more pertinent objects of the invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner by modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description describing the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.